Computational fluid-structure interaction of a restrained ogive-cylindrical body with a blunt elliptical base at a high incidence

The flow around an inclined tangent ogive-cylindrical body of a finite length with a blunt elliptical base, placed in a wind tunnel and allowed to yaw in the x-y plane, is studied computationally. The flow is three-dimensional, compressible, and laminar with a Reynolds number of 30 000 based on the body diameter and a Mach number of 0.2. The study covers the range of angles of attack from 0 degrees to 65 degrees, both for fixed and yaw-restrained configurations where solutions are determined after removal of initial disturbances. The flow around the fixed body, for alpha > 52 degrees and after disturbance removal, is nonstationary with large amplitude oscillations; for 0 degrees< alpha < 52 degrees the flow is almost steady with small nonstationary amplitude oscillations possibly due to the body's blunt end nonstationary wake. We identify a transition region between 45 degrees < alpha < 52 degrees where the attached wake behind the body end becomes detached. The resulting yaw response exhibits an intricate bifurcation structure that includes bistable periodic (finite amplitude) and nonstationary (small amplitude) limit cycles for moderate angles of attack, and nonstationary (finite amplitude) oscillations for high angles of attack. Investigation of the restraint torsion stiffness reveals a resonant periodic lock-in phenomena for low angles of attack which becomes quasiperiodic for a 40 degrees angle of attack.